This invention relates to a door latch assembly and particularly to a mechanism for disabling an actuator for a latch of the assembly when the door is locked while permitting free tactile operation of an outside door operator.
One type of commonly used latch assembly for a door contains an internal mechanism which is actuated by an outside operator such as, for example, a knob, a lever or a thumbpiece to withdraw and move the associated latch or bolt from a latched position to an unlatched position and thereby permit the opening of the door. The mechanism includes a rack and a pinion which are positioned in engagement so as to permit relative movement therebetween upon movement of the outside operator. This movement facilitates and controls the movement of the latch or bolt between latched and unlatched positions.
As illustrated and described in U.S. Pat. No. 2,021,565, a door latch assembly of this type includes a pinion which is connected to an external or outside lever handle to permit rotation of the pinion upon operation of the handle. A rack is positioned in meshing engagement with the pinion and is pivotally connected at one end to a bell crank lever which is also connected to a latch or locking bolt. When the handle is operated, the pinion rotates and drives the rack which, in turn, causes the bolt to move from the latched position to the unlatched position by virtue of pivotal movement of the bell crank lever.
If it is desired to lock the door latch, an internal or inside lever handle is moved from an unlocked position to a locked position to operate a linkage within the door latch assembly when the latch is in the latched position to pivot the rack away from and out of engagement with the pinion. Any subsequent movement of the outside lever handle will only result in rotation of the pinion but not in movement of the rack whereby the bolt remains and is locked in the latched position. When the inside handle is moved to the unlocked position, the linkage is manipulated to move the rack into meshing engagement with the pinion. The bolt can now be moved by operation of the outside handle.
When the latch is unlocked, the rack teeth mesh with the teeth of the pinion to reposition the rack and pinion for movement of the latch upon operation of the outside lever. If the teeth of the rack and pinion have become slightly misaligned during the period when they are separated, the teeth will not mesh smoothly. Due to the fragile nature of the teeth resulting from the physical size thereof and the materials used to form the rack and pinion, the misaligned meshing of the teeth could result in chipped or fractured teeth. Even when the teeth are of sufficient bulk and are composed of stronger materials, chipping or fracturing of the misaligned teeth could occur during re-meshing thereof.
In any event, this could eventually result in deficient operation, or complete lack of operability, of the door latch.
Additionally, if the pinion has been rotated to the operated position by operation of the outside handle at the same time that the inside lever is operated to move and return the rack into engagement with the pinion, the rack and pinion will be out of alignment by one or more teeth. In this condition, the outside handle will be in the operated position, that is pivoted downwardly, and will not return to the rest position. This will prevent normal and eventual depression of the outside lever downwardly to move the latch from the latched position to the unlatched position.
Further, if the pinion has been rotated while out of engagement with the rack to a position whereby the teeth of the rack and pinion are in interfacing alignment, when the rack is moved toward the pinion the teeth would not mesh but would move into butting engagement. This reaction will obviously render the actuating mechanism inoperable.
A similar rack and pinion actuating mechanism is also illustrated and described in U.S. Pat. No. 1,511,956.
Therefore, in view of the deficiency in a door latch having an actuating mechanism as set forth in the above-noted U.S. patents, there is a need for an actuating mechanism for a door latch which retains the operating components thereof in engagement even though the mechanism has been disabled during periods when the door latch is locked.